"Jock itch" refers to any itching groin rash of men and is not a medical term. There are many causes for "jock itch". When caused by a fungus, the rash is known as tinea cruris. The fungus causing tinea cruris is a microscopic plant that grows in the outer skin and prefers the moisture. When this fungus infects the feet, it's called "athlete's foot" (tinea pedis).
Contagion
Fortunately, tinea cruris is not contagious. Direct person-to-person spreading
is not a problem. The patient's own case of athlete's foot is the usual source
of infection and reinfection to the groin.
Prevention
Tinea cruris often comes back. Warmth and moisture encourage the fungus to grow.
You can prevent recurrences by drying thoroughly after bathing, wearing loose
cotton underwear, and dusting a bland powder on your groin once or twice daily.
After swimming, put on dry clothes right away; don't stay long in a wet
swimsuit.